1. Field of the Invention
The present invention relates to an inkjet recording apparatus for discharging ink from a recording head to record an image on a recording medium, and more particularly, an inkjet recording apparatus including a suction generating member for suctioning a recording medium to a platen.
2. Description of the Related Art
In a printer, a copying machine, a facsimile, a scanner, or a composite machine or system of those, a recording apparatus for forming an image on a recording medium, e.g. a recording paper, based on image information is used. As one embodiment of the recording apparatus, an inkjet recording apparatus which discharges ink to a recording medium from a discharge port of the recording head is widely used. “An image” in the present specification includes letters and symbols.
In order to perform stable recording, an inkjet recording apparatus needs to eliminate an influence of creases or wavy deformation (cockling) generated at the time when ink is fixed to a recording medium, as much as possible. Therefore, various methods to keep a space between the surface of the recording medium and a recording head constant have been proposed. Further, in consideration of the case when a recording medium originally curled due to humidity and the like is used, a method for preventing paper from floating toward the recording head from a platen in an image forming unit has also been proposed. That is, when the recording medium floats, the floating portion is contacted and rubbed by a recording head, a carriage or a surrounding guide mechanism, and thus a recording surface is damaged or smudged, which causes the reduction of an image quality. Further, the surface of discharge ports of the recording head (the surface on which discharge ports are arrayed) can be damaged by contacting the floating portion.
Accordingly, a configuration is proposed in which a suction portion for suctioning a recording medium to a platen is provided at the platen opposed to a recording head to suppress curling and cockling of the recording medium. Japanese Patent Application Laid-Open No. 2002-178542 discusses an apparatus using such a suction platen. The discussed apparatus includes many suction holes on a recording medium supporting surface of the hollowed platen and generates a negative pressure inside the platen using a suction generating member, e.g. a fan, to suction the recording medium to the platen.
Further, a configuration is known in which, when the inkjet recording apparatus performs a borderless recording (a marginless recording) which records an image up to an edge without providing margins, an image is recorded on a roll recording medium. Japanese Patent Application Laid-Open No. 11-321016 discusses an apparatus which records an image up to the outside region including the edge in the width direction of the recording medium and automatically cuts the recording medium having a recorded image in the conveyance direction by a cutter.
In this case, an ink receiver which is conventionally provided at a corresponding position on the platen is used to receive an ink discharged outward in the width direction of the recording medium. The ink receiver is recessed and has an opening on a conveyance supporting surface. Further, the ink receiver includes an ink absorbing material inside thereof. The ink receiver also includes a hole formed in the inside, from which the received ink is guided to a waste ink storage portion.
However, conventional inkjet recording apparatuses have the following problems. As the recording medium, paper or a film can be used, whose end portions are easily upwardly warped or curled depending on temperature and humidity environment. Thus, when such a recording medium is used, the available temperature and humidity environment is limited. That is, if the inkjet apparatus performs recording in an environment beyond the limitation of the temperature and humidity, an edge portion on a downstream side of the recording medium which is conveyed from a suction region of the platen, is upwardly warped up to where a fixed amount of the recording medium is conveyed. Thus, the recording medium is rubbed by contacting a recording head or a carriage so that an image quality is reduced.
A section up to where the fixed conveyance amount is conveyed, is the section up to where the edge portion of the recording medium is physically prevented from upwardly warping, or the edge portion of the recording medium hangs down under its own weight, which depends on a type of the recording medium. That is, the recording medium is conveyed with the upwardly warping edge portion until reaching the above point. As for a method for physically suppressing the upwardly warping, for example, a guide member in a conveying path is used, and a dustcover roller 32 provided at a dust cover 31 is used in an inkjet recording apparatus according to the embodiment of the present invention described below. Further, upwardly warping of the edge portion of the recording medium on the platen is reduced after passing this section, and thus the edge portion of the recording medium is not contacted and rubbed by the recording head or carriage.
In addition, high viscosity ink is used in order to maintain a high quality image in high speed recording, however, there are problems with respect to the high viscosity ink. In recent years, since a higher recording speed and a higher quality image are required, a high viscosity ink are more often used. When the high viscosity ink is used for recording, a preliminary discharge is generally performed before recording the image on the recording medium. In the preliminary discharge, ink is discharged not for the purpose of recording. When the viscosity of an ink in the discharge port of the recording head increases (viscosity increase) due to evaporation of a solvent, ink discharge from the recording head becomes unstable at the time of recording, and thus a recording image quality is reduced. The higher the viscosity of the ink, the more unstable the ink discharge becomes. Thus, when the high viscosity ink is used, the preliminary discharge is more frequently performed.
Further, all of discharge ports (nozzles) does not necessarily discharge the ink during a recording process depending on recording data. Moreover, a specific nozzle may not be used at all for a fixed period of time. Also, in the case of such nozzles, water contained in ink in the nozzle is evaporated so that the ink viscosity increases. Accordingly, when a discharge pulse is applied to a driving element of such nozzles at the time of recording, the ink can not be sufficiently discharged. Thus, the preliminary discharge has to be performed to prevent such a problem.
In the conventional inkjet recording apparatus, an ink receiver (a preliminary discharge receiver) that receives ink discharged by preliminary discharging is provided out of a recording region, that is, out of a paper passage region of a recording medium having a maximum size (a maximum width) which can be used. Therefore, the preliminary discharge before recording an image on a recording medium having a small size (a small width) must be performed each time by moving a recording head more than necessary to the ink receiver, which is separated from the recording medium more than needed. Thus, when an image is recorded on the recording medium having a small size, the recording head (the carriage) must be moved for the same distance as that for the medium having a maximum size, for every preliminary discharge. Therefore, the same time as that for the recording medium having a maximum size is required for a process of recording one sheet of the small size, so that the through put of the recording is reduced.